Etching parameter control system process

ABSTRACT

Focus and exposure parameters may be controlled in a lithographic process for manufacturing microelectronics by creating a complementary tone pattern of shapes and spaces in a resist film on a substrate. Corresponding dimensions of the resist shape and space are measured and the adequacy of focus or exposure dose are determined as a function of the measured dimensions. Etching parameters may also be controlled by creating a complementary tone pattern of etched shapes and spaces on a substrate. Corresponding dimensions of the etched shape and space are measured and the adequacy of etching parameters are determined as a function of the measured dimensions.

This is a divisional of copending application(s) Ser. No. 08/921,986filed on Aug. 28, 1997 allowed.

This application is related to U.S. application Ser. No. 08/919,998entitled Metrology Method Using Tone Reversed Pattern, and U.S.application Ser. No. 08/929,341 entitled Optically Measurable SerpentineEdge Tone Reversed Targets, and U.S. application Ser. No. 08/919,993entitled Optical Metrology Tool And Method Of Using Same, all filed oneven date herewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to manufacturing processesrequiring lithography and, more particularly, to monitoring oflithographic and etch process conditions used in microelectronicsmanufacturing which is particularly useful for monitoring patternfeatures with dimensions on the order of less than 0.5 micron.

2. Description of Related Art

Control of a lithographic imaging process requires the optimization ofexposure and focus conditions in lithographic processing of productwafers. Likewise, it is also important to optimize etching and otherparameters on product wafers. The current solution to the above problemsentails the collection and analysis of critical dimension measurementsusing SEM metrology on multiple pattern types at multiple locationswithin the chip, and from chip-to-chip. This method is slow, expensiveand error-prone. It usually requires the exposure of multiplefocus-exposure and etching matrices on product wafers.

Generally, because of the variations in exposure and focus, patternsdeveloped by lithographic processes must be continually monitored ormeasured to determine if the dimensions of the patterns are withinacceptable range. The importance of such monitoring increasesconsiderably as the resolution limit, which is usually defined asminimum features size resolvable, of the lithographic process isapproached. The patterns being developed in semiconductor technology aregenerally in the shape of lines both straight and with bends, having alength dimension equal to and multiple times the width dimension. Thewidth dimension, which by definition is the smaller dimension, is of theorder of 0.1 micron to greater than 1 micron in the current leadingsemiconductor technology. Because the width dimension is the minimumdimension of the patterns, it is the width dimension that challenges theresolution limits of the lithographic process. In this regard, becausewidth is the minimum and most challenging dimension to develop, it isthe width dimension that is conventionally monitored to assessperformance of the lithographic process. The term "bias" is used todescribe the change in a dimension of a feature from its nominal value.Usually the bias of interest is the change in the smallest of thedimensions of a given feature. Further, the term "bias" is invariablyused in conjunction with a process such as resist imaging, etching,developing etc. and described by terms such as image bias, etch bias,print bias etc.

Monitoring of pattern features and measurement of its dimensions(metrology) is typically performed using either a scanning electronmicroscope (SEM) or an optical tool. Current practice in thesemiconductor industry is to use topdown SEMs for the in-line metrologyof all critical dimensions below approximately 0.7 um. Unfortunately,SEM metrology is expensive to implement, relatively slow in operationand difficult to automate. At best, algorithms that attempt to determinethe absolute dimensions at a fixed pattern height (e.g., the interfaceof the pattern with the underlying substrate), are accurate to only30-50 nm--a substantial fraction, if not all, of current criticaldimension tolerance. The need to measure individual features below 0.25um poses a serious challenge not just to their imaging capability, butto all the subsystems required for automated measurement--patternrecognition, gate placement, edge detection, and the like.

Although optical metrology overcomes the above drawbacks associated withSEM and AFM metrology, optical metrology systems are unable to resolveadequately for measurement of feature dimensions of less than about 1micron. Additionally, false sensitivity has limited the applicability ofoptical microscopy to sub-micron metrology on semiconductor productwafers.

The degradation of optical resolution as chip dimensions approach thewavelength of light precludes the application of optical microscopy tothe measurement of individual chip features. Even setting aside theaccuracy requirement for in-line metrology, the blurred images ofadjacent edges overlap and interfere, and the behavior of the intensityprofile of the image no longer bears any consistent relationship to theactual feature on the wafer. It is this loss of measurement"consistency" (definable as a combination of precision and sensitivity)that establishes the practical limit of conventional optical metrologyin the range of 0.5-1.0 um.

With regard to false sensitivity, the thin films used in semiconductormanufacturing vary widely in their optical characteristics. Opticalmetrology is susceptible to variations in the thickness, index ofrefraction, granularity and uniformity of both the patterned layer andunderlying layers. Film variations that affect the optical image can befalsely interpreted as variations in the pattern dimension.

Improvements in monitoring bias in lithographic and etch processes usedin microelectronics manufacturing have been disclosed in U.S. patentapplication Ser. Nos. 08/359797, 08/560720 and 08/560851. In Ser. No.08/560851, a method of monitoring features on a target using an imageshortening phenomenon was disclosed. In Ser. No. 08/560720, targets andmeasurement methods using verniers were disclosed to measure bias andoverlay error. In these applications, the targets comprised arrays ofspaced, parallel elements having a length and a width, with the ends ofthe elements forming the edges of the array. While the targets andmeasurement methods of these applications are exceedingly useful, theyrely on the increased sensitivity to process variation provided by imageshortening.

Accordingly, there is still a need for a method of monitoring patternfeatures of arbitrary shape with dimensions on the order of less than0.5 micron, and which is inexpensive to implement, fast in operation andsimple to automate. There is a need for a process for determining biaswhich enables in-line lithography/etch control using optical metrology,and wherein SEM and/or AFM metrology is required only for calibrationpurposes.

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide a measurementtool, test pattern and evaluation method for determining exposure andfocus conditions whereby one pattern group is capable of distinguishingbetween exposure and focus problems in semiconductor pattern processing.

It is another object of the present invention to provide a measurementtool, test pattern and evaluation method for determining etching timeand rate conditions and other etching process conditions whereby onepattern group is capable of distinguishing between etching time and rateproblems and other etching process problems in semiconductor patternprocessing.

A further object of the invention is to provide a method of evaluatingfocus-exposure and etching parameters which may be used with existingmetrology instruments and exposure and etching equipment.

It is yet another object of the present invention to provide a method ofevaluating focus-exposure and etching parameters which is easy andinexpensive to utilize.

It is also an object of the present invention to provide a method andtarget for determining bias and overlay error in patterns deposited as aresult of lithographic processes.

It is a further object of the present invention to provide a method andtarget which combines measurement of bias and overlay error in depositedpatterns, and which utilize little space on a wafer substrate.

It is a further object of the present invention to provide a process formeasuring bias using targets which are intentionally not resolved by themetrology tool employed.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

SUMMARY OF THE INVENTION

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which relates to aprocess for controlling focus or exposure dose parameters in alithographic process comprising first exposing a complementary tonepattern onto a resist film layer having a resist threshold disposed on asubstrate. The complementary tone pattern comprises a first patternportion having a shape which corresponds to an area on the resist filmhaving an exposure dose below the resist threshold of the resist filmand a second pattern portion having a space which corresponds to an areaon the resist film having an exposure dose above the resist threshold ofthe resist film. The shape and space have corresponding dimensions of aknown relationship, for example, equal dimensions. Next, there iscreated on the resist film a latent image of the space and an unexposedarea within a latent image of the shape. Then the dimension on thelatent image space and the dimension on the unexposed area within thelatent image shape are measured. Finally, the adequacy of focus orexposure dose parameters is determined as a function of the measureddimensions of the latent image shape and space.

In another aspect, the present invention relates to a process forcontrolling focus or exposure dose parameters in a lithographic processcomprising first exposing a complementary tone pattern onto a resistfilm layer having a resist threshold disposed on a substrate. Thecomplementary tone pattern comprises a first pattern portion having ashape which corresponds to an area on the resist film having an exposuredose below the resist threshold of the resist film and a second patternportion having a space which corresponds to an area on the resist filmhaving an exposure dose above the resist threshold of the resist film.The shape and space have corresponding dimensions of a knownrelationship, for example, equal dimensions. There is subsequentlycreated on the resist film a latent image of the space and an unexposedarea within a latent image of the shape. Next, one contacts the latentimage space and the shape on the resist film with a developer to removeselected portions of the resist film to create developed imagescorresponding to the latent image space and the shape, respectively.Then, the dimension on the developed image shape and the dimension onthe developed image space are measured. The adequacy of focus orexposure dose parameters is determined as a function of the measureddimensions of the developed image shape and space.

The process may include determining the difference of the measureddimensions on the developed image shape and space and, if the differenceis outside of a predetermined tolerance, modifying the exposure doseparameter of the process. Preferably, the steps are repeated until thedifference of the measured dimensions on the developed image shape andspace is within the predetermined tolerance.

The process may also include determining the sum of the measureddimensions on the developed image shape and space and, if the sum isoutside of a predetermined tolerance, modifying the focus parameter ofthe process. Preferably, the steps are repeated until the sum of themeasured dimensions on the developed image shape and space is within thepredetermined tolerance.

In one preferred embodiment, the shape and space are rectangular havinga width and a length, and the focus or exposure dose parameters aredetermined as a mathematical function of the width or length dimensionson the developed image shape and space. The rectangular shape and spacemay have a width and a length greater than the width, and the focus orexposure dose parameters may be determined as a mathematical function ofthe length dimensions on the developed image shape and space.

In another preferred embodiment, the shape and space have opposed pointsformed by acute angles, and the focus or exposure dose parameters aredetermined as a mathematical function of the distances between theopposed points formed by acute angles on the developed image shape andspace.

The process may further include the step of mapping measuredcorresponding dimensions of developed image shapes and spaces, and thefunction of the measured corresponding dimensions, over a plurality offocus and exposure conditions. If the determination of adequacy of focusor exposure dose parameters is outside of a predetermined tolerance, thefocus or exposure dose parameter of the process may be modified byutilizing information from the mapping step.

In yet another aspect, the present invention provides a process forcontrolling etching or other parameters in an etching process comprisingfirst providing a substrate having an overlying resist film layer with acomplementary tone developed image pattern comprising a first patternportion having a developed image shape made of the resist film, and asecond pattern portion having a developed image space removed from theresist film. The shape and space have corresponding dimensions of aknown relationship, for example, equal dimensions. Next, there isprovided an etchant for removing substrate material not covered by theresist film, and the developed image shape and space is contacted withthe etchant for a desired time to create an etched image of thedeveloped image shape on the substrate and an etched image of thedeveloped image space on the substrate. The dimension on the etchedimage shape and the dimension on the etched image space are measured.The adequacy of etching or other parameters is determined as a functionof the measured dimensions on the etched image shape and space.

The process may include determining the difference of the measureddimensions on the etched image shape and space and, if the difference isoutside of a predetermined tolerance, modifying the etching timeparameter of the process. Preferably, the steps are repeated until thedifference of the measured dimensions on the etched image shape andspace is within the predetermined tolerance.

The process may also include determining the sum of the measureddimensions on the etched image shape and space and, if the sum isoutside of a predetermined tolerance, modifying a parameter of theprocess other than the etching time. Preferably, the steps are repeateduntil the sum of the measured dimensions on the etched image shape andspace is within the predetermined tolerance

In one preferred embodiment, the shape and space are rectangular havinga width and a length, and the focus or exposure dose parameters aredetermined as a mathematical function of the width or length dimensionson the etched image shape and space. The rectangular shape and space mayhave a width and a length greater than the width, and wherein the focusor exposure dose parameters are determined as a mathematical function ofthe length dimensions on the etched image shape and space.

In another preferred embodiment, the latent image shape and space haveopposed points formed by acute angles in the images, and the focus orexposure dose parameters are determined as a mathematical function ofthe distances between the opposed points formed by acute angles on theetched image shape and space.

The process may further include the step of mapping measuredcorresponding dimensions of etched image shapes and spaces, and thefunction of the measured corresponding dimensions, over a plurality ofetching conditions. If the determination of adequacy of etchingparameters is outside of a predetermined tolerance, the etchingparameter of the process may be modified by utilizing information fromthe mapping step.

In another aspect, the present invention relates to a process forcontrolling focus or exposure dose parameters in a lithographic processcomprising the steps of:

a) exposing a plurality of a first set of complementary tone patternsonto a resist film layer having a resist threshold disposed on asubstrate, each of said first set of complementary tone patternscomprising: i) a first pattern portion having a shape which correspondsto an area on the resist film having an exposure dose below the resistthreshold of the resist film and ii) a second pattern portion having aspace which corresponds to an area on the resist film having an exposuredose above the resist threshold of the resist film, said shape and spacehaving corresponding dimensions, each of said exposed first set ofcomplementary tone patterns being exposed on said resist film underdifferent focus or exposure dose conditions;

b) measuring said dimensions of image shapes and spaces on each of saidexposed first set of complementary tone patterns;

c) determining optimum focus or exposure dose conditions based on themeasurements of step (b);

d) determining the dependence of focus or exposure dose conditions onsaid dimensions of the image shapes and spaces near the optimum focus orexposure dose conditions determined in step (c);

e) exposing one or more of a second set of complementary tone patternsonto a resist film layer having a resist threshold disposed on asubstrate, each of said second set of complementary tone patternscomprising: i) a first pattern portion having a shape which correspondsto an area on the resist film having an exposure dose below the resistthreshold of the resist film and ii) a second pattern portion having aspace which corresponds to an area on the resist film having an exposuredose above the resist threshold of the resist film, said shape and spacehaving corresponding dimensions;

f) measuring said dimensions of image shapes and spaces on each of saidexposed second set of complementary tone patterns; and

g) determining adequacy of focus or exposure dose parameters on each ofsaid exposed second set of complementary tone patterns based on themeasurements and determinations of steps (a)-(d).

The process may further include the step of:

h) establishing focus or exposure dose parameters for subsequentexposure of a third set of complementary tone patterns by applying ameasurement of said dimensions of image shapes and spaces on at leastone of said exposed second set of complementary tone patterns to thedependence of focus or exposure dose conditions made in step (d).

The process may also include the further step of:

h) establishing focus or exposure dose parameters for subsequentexposure of a third set of complementary tone patterns by applying ameasurement of said dimensions of image shapes and spaces on at leastone of said exposed second set of complementary tone patterns to thedependence of focus or exposure dose conditions made in step (d) topredict a new focus or exposure dose parameter, and taking an average ofthe predicted new focus or exposure dose parameter and the focus orexposure dose parameter of said at least one of said exposed second setof complementary tone patterns.

Said dimensions of said shape and space may be nominally identical, suchthat the adequacy of focus or exposure dose parameters are determinedbased on the dimensions on said image shape and space.

The measuring of the dimensions of the image shapes and spaces on eachof the exposed first and second sets of complementary tone patterns insteps (b) and (f) is by the steps of:

i) creating on said resist film a latent image of each space and anunexposed area within a latent image of each shape;

ii) measuring the dimension on each latent image space; and

iii) measuring the dimension on the unexposed area within each latentimage shape.

Alternatively, the measuring of the dimensions of the image shapes andspaces on each of the exposed first and second sets of complementarytone patterns in steps (b) and (f) is by the steps of:

i) creating on said resist film a latent image of each space and anunexposed area within a latent image of each shape;

ii) contacting each latent image space and shape on the resist film witha developer to remove selected portions of the resist film to createdeveloped images corresponding to each latent image space and shape,respectively;

iii) measuring the dimension on each developed image shape; and

iv) measuring the dimension on each developed image space.

In one embodiment, said shape and space are rectangular having a widthand a length, for example with a length greater than said width, suchthat the adequacy of focus or exposure dose parameters are determinedbased on the width or length dimensions on said image shape and space.In another embodiment, said shape and space have opposed points formedby acute angles, for example with a length greater than said width, suchthat the adequacy of focus or exposure dose parameters are determined asa mathematical function of the distances between the opposed pointsformed by acute angles on said image shape and space.

In a related aspect, the present invention provides a process forcontrolling etching or other parameters in a lithographic processcomprising the steps of:

a) providing a plurality of a first set of complementary tone developedimage patterns on a resist film layer on a substrate, each of said firstset of complementary tone patterns comprising: i) a first patternportion having a developed image shape made of said resist film and ii)a second pattern portion having a developed image space removed fromsaid resist film, said shape and space having corresponding dimensions,

b) etching each of said developed first set of complementary tonepatterns under different etching conditions to create an etched image ofsaid developed image shape and an etched image of said developed imagespace;

c) measuring the dimensions of the etched image shapes and spaces oneach of said exposed first set of complementary tone patterns;

d) determining optimum etching or other conditions based on themeasurements of step (c);

e) determining the dependence of etching or other conditions on saiddimensions of the image shapes and spaces near the optimum etching orother conditions determined in step (d);

f) providing one or more of a second set of complementary tone developedimage patterns on a resist film layer on a substrate, each of saidsecond set of complementary tone patterns comprising: i) a first patternportion having a developed image shape made of said resist film and ii)a second pattern portion having a developed image space removed fromsaid resist film, said shape and space having corresponding dimensions;

g) measuring said dimensions of the etched image shapes and spaces oneach of said exposed second set of complementary tone patterns; and

h) determining adequacy of etching or other parameters on each of saidexposed second set of complementary tone patterns based on themeasurements and determinations of steps (a)-(e).

The process may further include the step of:

i) establishing etching or other parameters for subsequent etching of athird set of complementary tone patterns by applying a measurement ofsaid dimensions of image shapes and spaces on at least one of saidetched second set of complementary tone patterns to the dependence ofetching or other conditions made in step (e).

The process may also include the further step of:

i) establishing etching or other parameters for subsequent etching of athird set of complementary tone patterns by applying a measurement ofsaid dimensions of image shapes and spaces on at least one of saidetched second set of complementary tone patterns to the dependence ofetching or other conditions made in step (e) to predict a new etching orother parameter, and taking an average of the predicted new etching orother parameter and the etching or other parameter of at least one ofsaid etched second set of complementary tone patterns.

The dimensions of said shape and space may be nominally identical, suchthat the adequacy of etching or other parameters are determined based onthe dimensions on said image shape and space. In one embodiment, saidshape and space are rectangular having a width and a length, for examplewith a length greater than said width, such that the adequacy of etchingor other parameters are determined based on the width or lengthdimensions on said image shape and space. In another embodiment, saidshape and space have opposed points formed by acute angles, for examplewith a length greater than said width, such that the adequacy of etchingor other parameters are determined as a mathematical function of thedistances between the opposed points formed by acute angles on saidimage shape and space.

In yet another aspect, the present invention relates to a target formeasurement of parameters on a substrate formed by a lithographicprocess comprising a contrasting area on said substrate having a linearedge, and a contrasting array of elements on said substrate. The arraycomprises a plurality of spaced parallel elements contrasting with saidsubstrate and extending from a first element to a last element, each ofsaid elements having length and width, ends of the contrasting elementsbeing aligned along parallel lines forming opposite array edges, thelength of the contrasting elements comprising the array width and thedistance between opposite far edges of the first and last elementscomprising the array length, the linear edge of said contrasting areacontacting each of said contrasting elements along one edge of saidarray. The array width is measurable by microscopy without resolution ofindividual elements of the array to determine a parameter of saidsubstrate.

The linear edge of said contrasting area may extend beyond at least oneof said first or last elements and said contrasting area may furtherinclude a portion contacting said last element along the opposite faredge. The array width is also measurable by microscopy withoutresolution of individual elements of the array to determine a parameterof said substrate. The width of each element may be constant over theelement length, or the width of each element may taper down from thecontrasting area linear edge over the element length.

The target may further include a second contrasting array of elements onsaid substrate. Said second array may comprise a plurality of spacedparallel elements contrasting with said substrate and extending from afirst element to a last element, each of said elements having length andwidth, ends of the contrasting elements being aligned along parallellines forming opposite array edges, the length of the contrastingelements comprising the second array width and the distance betweenopposite far edges of the first and last elements comprising the secondarray length. Said second contrasting array is spaced from the firstarray edge opposite the linear edge of said contrasting area, and thesecond array width is measurable by microscopy without resolution ofindividual elements of the second array to determine a parameter of saidsubstrate.

Preferably, the first and second array edges are parallel, and thelengths of said first and second arrays are substantially equal, whereinsaid first and second arrays are spaced from each other by a distanceequal to the width of said arrays.

The target may further include a second linear edge on said contrastingarea parallel to and spaced from said first linear edge on a sideopposite said first contrasting array, and a second contrasting array ofelements on said substrate. Said second array comprises a plurality ofspaced parallel elements contrasting with said substrate and extendingfrom a first element to a last element, each of said elements havinglength and width, ends of the contrasting elements being aligned alongparallel lines forming opposite array edges, the length of thecontrasting elements comprising the second array width and the distancebetween opposite far edges of the first and last elements comprising thesecond array length, the second linear edge of said contrasting areacontacting each of said contrasting elements along one edge of saidsecond array. The second array width is measurable by microscopy withoutresolution of individual elements of the second array to determine aparameter of said substrate.

Preferably, the first and second array edges are parallel, and thelengths of said first and second arrays are substantially equal, whereinsaid first and second arrays are spaced from each other by a distanceequal to the width of said arrays.

The target may further include a third contrasting array of elements onsaid substrate. Said third array comprises a plurality of spacedparallel elements contrasting with said substrate and extending from afirst element to a last element, each of said elements having length andwidth, ends of the contrasting elements being aligned along parallellines forming opposite array edges, the length of the contrastingelements comprising the third array width and the distance betweenopposite far edges of the first and last elements comprising the thirdarray length. Said third contrasting array is spaced from the firstarray edge opposite the first linear edge of said contrasting area, andthe third array width is measurable by microscopy without resolution ofindividual elements of the third array to determine a parameter of saidsubstrate.

Preferably, the first and third array edges are parallel, and thelengths of said first and third arrays are substantially equal, whereinsaid first and third arrays are spaced from each other by a distanceequal to the width of said arrays.

The target may further include a second contrasting area having a thirdlinear edge on said second contrasting area parallel to and spaced fromsaid first and second linear edges of said first contrasting area, saidthird linear edge contacting each of the contrasting elements of saidthird contrasting array along an edge of said third array on a sideopposite said first contrasting array. Preferably, the first and thirdarray edges are parallel, the width of said first and third arrays aresubstantially equal, and said first and third arrays are spaced fromeach other by a distance equal to the width of said arrays, wherein thewidth of said first and contrasting second areas is normal to the linearedges of said areas and wherein said first and second contrasting areashave lengths equal to the lengths of said arrays.

In a related aspect, the present invention provides a method ofmeasuring parameters on a substrate formed by a lithographic processcomprising the steps of:

a) providing a target comprising a contrasting area formed on asubstrate by a lithographic process, said contrasting area having alinear edge; and a contrasting array of elements on said substrate, saidarray comprising a plurality of spaced parallel elements contrastingwith said substrate and extending from a first element to a lastelement, each of said elements having length and width, ends of thecontrasting elements being aligned along parallel lines forming oppositearray edges, the length of the contrasting elements comprising the arraywidth and the distance between opposite far edges of the first and lastelements comprising the array length, the linear edge of saidcontrasting area contacting each of said contrasting elements along oneedge of said array;

b) resolving said array edges without resolving individual elements ofthe array; and

c) measuring the position of said array edges to determine a desiredparameter of said substrate.

Preferably, step (c) comprises determining the position of a centerlinebetween two of said array edges. The method may further include thesteps of:

i) providing a second contrasting array of elements on said substrate,said second array comprising a plurality of spaced parallel elementscontrasting with said substrate and extending from a first element to alast element, each of said elements having length and width, ends of thecontrasting elements being aligned along parallel lines forming oppositearray edges, the length of the contrasting elements comprising thesecond array width and the distance between opposite far edges of thefirst and last elements comprising the second array length, and whereinsaid second contrasting array is spaced from the first array edgeopposite the linear edge of said contrasting area;

ii) resolving said first and second array edges without resolvingindividual elements of the arrays; and

iii) measuring the position of said first and second array edges todetermine a desired parameter of said substrate.

The method may further include the steps of:

i) further including a second linear edge on said contrasting areaparallel to and spaced from said first linear edge on a side oppositesaid first contrasting array, and a second contrasting array of elementson said substrate, said second array comprising a plurality of spacedparallel elements contrasting with said substrate and extending from afirst element to a last element, each of said elements having length andwidth, ends of the contrasting elements a being aligned along parallellines forming opposite array edges, the length of the contrastingelements comprising the second array width and the distance betweenopposite far edges of the first and last elements comprising the secondarray length, the second linear edge of said contrasting area contactingeach of said contrasting elements along one edge of said second array;

ii) resolving said first and second array edges without resolvingindividual elements of the arrays; and

iii) measuring the position of said first and second array edges todetermine a desired parameter of said substrate.

Step (iii) may comprise determining the position of a centerline betweentwo of said array edges.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a plan view of an embodiment of complementary rectangularshape (opaque) and space (transparent) patterns on a mask used for photolithography.

FIG. 2 is a plan view of an embodiment of complementary triangular shape(opaque) and space (transparent) patterns on a mask used for photolithography.

FIG. 3 is an enlargement of one embodiment of the apex of the trianglesof FIG. 2 made by a single-sided stepping pattern.

FIG. 4 is an enlargement of another embodiment of the apex of thetriangles of FIG. 2 made by a symmetrical stepping pattern.

FIG. 5 shows a portion of the photolithography process for oneembodiment of the present invention utilizing an isolated opaque shapeon an essentially transparent mask.

FIG. 6 shows a portion of the photolithography process for anotherembodiment of the present invention utilizing an isolated transparentshape on an essentially opaque mask.

FIG. 7 is a plan view of an embodiment of complementary rectangularshape (opaque) and space (transparent) latent and developed imagepatterns on the resist layer of a substrate made from the mask of FIG.1.

FIG. 8 is a plan view of an embodiment of complementary triangular shape(opaque) and space (transparent) latent and developed image patterns onthe resist layer of a substrate made from the mask of FIG. 2.

FIG. 9 is a plot of measured line (shape) widths as a function of focusunder different exposures, for a nominal line width of the type shown inFIG. 7 of 0.3 microns.

FIG. 10 is a plot of measured space widths as a function of focus underdifferent exposures, for a nominal space width of the type shown in FIG.7 of 0.3 microns.

FIG. 11 is a plot of the difference of measured line and space widthsshown in FIGS. 9 and 10, as a function of focus.

FIG. 12 is a plot of the sum of measured line and space widths shown inFIGS. 9 and 10, as a function of focus.

FIG. 13 is a plot of measured line lengths as a function of focus underdifferent exposures, for a nominal line length of the type shown in FIG.7 of 1 micron.

FIG. 14 is a plot of measured space lengths as a function of focus underdifferent exposures, for a nominal space length of the type shown inFIG. 7 of 1 micron.

FIG. 15 is a plot of the difference of measured line and space lengthsshown in FIGS. 13 and 14, as a function of focus.

FIG. 16 is a plot of the sum of measured line and space lengths shown inFIGS. 13 and 14, as a function of focus.

FIG. 17 is a plan view of an embodiment of complementary rectangularshape (opaque) and space (transparent) etched image patterns on theresist layer of a substrate made from the mask of FIG. 1 and latent anddeveloped images of FIG. 7.

FIG. 18 is a plan view of an embodiment of complementary triangularshape (opaque) and space (transparent) etched image patterns on theresist layer of a substrate made from the mask of FIG. 2 and latent anddeveloped images of FIG. 8.

FIG. 19 is a flow diagram of the combined preferred processes of thepresent invention.

FIG. 20 is a flow diagram of a manufacturing control system utilizingtone reversed patterns of the present invention to control focus andexposure dose settings.

FIG. 21 is a flow diagram of a manufacturing control system utilizingtone reversed patterns of the present invention to control etching andother settings.

FIG. 22a is a plan view of a target comprising a single contrastingstraight edge.

FIG. 22b shows the target of FIG. 22a having thereon a serpentine edgecomprising an array of individual spaced, parallel line elements.

FIG. 23a is a plan view of a target similar to FIG. 22b.

FIG. 23b depicts the target of FIG. 23a as seen when the individualarray elements are not resolved.

FIG. 24 depicts a target similar to FIG. 22b, except that the individualarray lines are tapered.

FIG. 24a is an enlargement of one embodiment of the tapered array linesof FIG. 24.

FIG. 24b is an enlargement of another embodiment of the tapered arraylines of FIG. 24.

FIG. 25 is a plan view of an embodiment of a target using contrastingtone reversing arrays.

FIGS. 26a, 26b, 27a, 27b and 28a, 28b depict plan views of other targetsutilizing contrasting tone reversing arrays.

FIG. 29 is a plot of measured shape length separation as an function ofexpose dose for the target shown in FIG. 25.

FIG. 30 is a plot of space length separation relative to nominal for thetarget shown in FIG. 25.

FIG. 31 is a plot of a function of the shape and space measurements as afunction of defocus for the targets of FIG. 25.

FIG. 32 is a plot of a function of the shape and space measurements as afunction of defocus for the targets of FIG. 25.

FIG. 33 is a plot of space length separation for the target shown inFIG. 25.

FIG. 34 is a plot of shape length separation relative to nominal for thetarget shown in FIG. 25.

FIG. 35 is a plot of a function of the shape and space measurements as afunction of defocus for the targets of FIG. 25.

FIG. 36 is a plot of a function of the shape and space measurements as afunction of defocus for the targets of FIG. 25.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1-36 of the drawings in whichlike numerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

The present invention utilizes a pattern control system based on themeasurement of complementary tone patterns, i.e., patterns in which thetone is reversed. The "tone" of a lithographic pattern is determined bythe presence or absence of resist material which is normally depositedin a layer or film on the surface of the substrate to be etched.Patterns are either resist shapes on a clear background or the absenceof resist shapes (i.e., spaces) in a background of resist material.Complementary tone patterns can be formed by interchanging the areasthat are exposed during the lithographic process.

These tone patterns may be created in resist material by preparing maskswith opaque and transparent areas corresponding to the shapes or spacesto be created on the resist material, and then using a source ofradiation on one side of the mask to illuminate and project the maskshapes and spaces on the resist layer on the opposite side of the mask.Resist layers have a resist threshold. When exposed to radiation orenergized above the resist threshold, a latent image is formed. Nolatent image is created when the level of exposure to radiation is belowthe resist threshold. These mask shapes and spaces form correspondinglatent images on the resist layer. The latent images are manifested bychanges in film reflectivity and may be optically detected beforedeveloping by visual observation, for example, with a microscope.

Alternatively, complementary tone patterns may be exposed on resistmaterial by other types of masks, for example, phase shift masks, orother methods, for example, an electron beam exposure tool. Instead ofusing masks, these other methods may form the shapes and spaces bymultiple exposure of pixels or other discrete forms.

After the latent images on the resist material are developed, an etchantis used to attack the substrate not covered by the resist material. Theetched areas or spaces of the substrate form trenches in the substrate,leaving the unetched areas or shapes as raised structures adjacent tothe trenches. The etched images are formed by the walls between theraised areas and trenches, and will also form complementary etchedimages corresponding to the complementary tone patterns on the resistfilm.

As shown in FIG. 1, a mask 42 substantially transparent to anilluminating light source used for exposing resist films has thereontranslucent or opaque areas 22, 24 which substantially block thetransmission of the light source. These will be referred to herein as"opaque" mask areas, although the degree of opacity is only thatsufficient to distinguish the opaque area from the substantiallytransparent area. Opaque mask area 24 is shown having a substantiallytransparent area 26 in the shape of a rectangle. A complementaryrectangular opaque mask area 24 on an otherwise substantiallytransparent portion of substrate 42 is also shown. The width W₁ ofopaque mask area 22 is equal to the width W_(s) of transparent space 26.Likewise, the length L₁ of opaque mask area 22 is equal to the lengthL_(s) of transparent area 26. The opaque and transparent areas having atleast one corresponding dimension, and preferably all correspondingdimensions, are complementary mask areas.

Another example of complementary mask patterns is depicted in FIG. 2where a triangular shaped transparent area 26a in an opaque mask area24a has dimensions corresponding to the triangular shaped opaque maskarea 22a on a transparent mask background. Both the transparent area 26aand the opaque area 22a have opposing ends in the form of acute angleswith the distance between the opposed points comprising the length L₁.These opposing ends are shown on the opaque triangle 22a as ends 28, 30,and in the transparent triangle 26a as ends 29, 31.

The relationship between the corresponding dimensions of the mask shapeand space should be known. In FIGS. 1 and 2, all of the correspondingmask shape and space dimensions are equal.

As shown more clearly in FIGS. 3 and 4, the actual tapered or angledsides forming the end points of the triangle shaped end 30 as shown inFIG. 2 can be formed by stepping the patterns in increments of theminimum design grid, typically 25 nm. A single-sided stepping patterncan be used as shown on end 30b in FIG. 3 or a symmetrical steppingpattern can be used as shown on end 30c in FIG. 4. The single sidedstepping (FIG. 3) has the advantage that a more gradual taper ispossible, resulting in a more acute angle for the end of the shape.Likewise, the mask transparent area is also formed by stepping patternin the surrounding opaque mask material.

The lithographic process preferably employed in connection with thepresent invention is shown in FIGS. 5 and 6. In each of these preferredembodiments, a mask or reticle pattern is transferred via spatiallymodulated light 40 through a lens 62 to create an aerial image which istransferred to the resist film on a substrate. In FIG. 5, this is shownas an isolated opaque area 44 on a transparent mask background 42 ofintensity 56 which forms aerial image 64. In FIG. 6, this is shown asopaque areas 52 and 54 on transparent mask 42 having an isolatedtransparent area between opaque areas of intensity 60, which formsaerial image 68.

Those segments of the absorbed aerial image, whose energy exceeds athreshold energy of chemical bonds in the photo-active component (PAC)of the resist material, create a latent image in the resist film. Insome resist systems, the latent image is formed directly by the PAC. Inothers (so-called acid-catalyzed resist), the photo-chemical interactionfirst generates acid which reacts with other resist components during apost-exposure bake to form the latent image. In either case, the latentimage marks the volume of resist material that either is removed duringthe development process (in the case of positive resist) or remainsafter development (in the case of negative resist) to create athree-dimensional pattern in the resist film. The remaining resistmaterial is shown in FIGS. 5 and 6 as 70 and 78, respectively, onsubstrate 80.

Subsequently, an etchant for the substrate which is unreactive with theresist film is then applied and etches the substrate in the area inwhich the resist film is not present. The etched image is shown in FIG.5 as shape 84 on substrate base 82 and in FIG. 6 as space 92 onsubstrate base 82.

All of the mask materials, light sources, resist materials, developersand etchants, as well as the processes for using them, are well known inthe art. Evaluation and measurement of the shapes and spaces may be madeby optical microscopy (for latent images) or optical or scanningelectron microscopy (for developed images).

The latent and developed images formed in the resist film material areshown in FIGS. 7 and 8. In FIG. 7, rectangular latent image 122 isformed on substrate 80 which corresponds to the rectangular opaque area22 in FIG. 1. Likewise, latent image 124, corresponding to opaque maskarea 24, has rectangular space 126 corresponding to rectangulartransparent area 26. After developing, the latent images result indeveloped resist image areas of the same shape and configuration as onsubstrate 80. Rectangular developed resist shape 122 is disposed on abackground free of resist material on the right hand portion ofsubstrate 80. The length and width of developed image 122 are shown asL₁ and W₁, respectively. Complementary rectangular area 126 is free ofresist material in the background of resist material 124. The length andwidth of developed image space 126 are shown as L_(s) and W_(s),respectively. The complementary shapes and spaces utilized in thepresent invention should have corresponding dimensions, i.e., thereshould be at least one dimension on a shape which can be related to adimension on a space. For example, the dimension on the shape may be amultiple of the corresponding dimension on the space. Shape 122 andspace 126 may also be of equal size.

In FIG. 8, triangular latent image 122a on substrate 80 corresponds totriangular opaque mask area 22a in FIG. 2, and after developing,produces triangular resist material area 122a of length L₁ on abackground free of resist material. Latent image 124a with triangularspace 126a corresponds to opaque mask area 24a in FIG. 2 and, afterdeveloping, produces a triangular area 126a free of resist material oflength L_(s) on a background of resist material 124a. Triangular space126a free of resist material is complementary to triangular area 122a ofresist material.

In order to distinguish between the complementary patterns, "shape" whenused in connection with a latent image or resist layer will refer to: i)an area of a latent image which has an exposure dose below the resistthreshold of the resist film, or ii) after development of the latentimage, the area of resist material which remains on the substrate and issurrounded by an area free of resist material. The terms shape, line andisland have equivalent meanings as used herein. "Space" when used inconnection with a latent image or resist layer will refer to: i) an areaof a latent image which has an exposure dose above the resist thresholdof the resist film, or ii) after development of the latent image, thearea on the substrate which is free of resist material and is surroundedby an area of resist material. The terms space, trench and trough haveequivalent meanings as used herein. Contact refers to the case where thedimensions of the space are approximately equal in X and Y directions.Since positive and negative resist materials react opposite to oneanother when subjected to exposure doses above and below the resistthreshold, the above definition, when applied to positive resistmaterials will be reversed when applied to negative resist materials.Throughout this specification, examples and discussion will be ofpositive resist material, unless otherwise noted.

It has been found that, in the regime of interest for controllinglithographic patterning, the dimensions of latent image or resist shapesand latent image or resist spaces change in opposite directions withexposure dose. Exposure dose is the combination of time of exposure ofthe aerial image on the resist film and the intensity of the lightsource utilized. That is, as the exposure dose is reduced, the length ofthe latent image or resist space decreases as compared to the true ornominal length of the latent image or resist space which would have beencreated under ideal exposure dose. The unexposed area within a latentimage or the resist shape is simultaneously increased in dimension withdecreasing exposure dose by the illumination source, as compared to thedimension of the shape under ideal exposure.

With increasing exposure dose, it has been found that the dimensions ofthe latent image or resist space will increase, and the dimensions ofthe unexposed area within a latent image or the resist shape willdecrease.

Unlike the changes with exposure dose, it has been found that thedimensions of the latent image and resist spaces and the dimensions ofthe unexposed area within a latent image and the resist shapes change inthe same direction with different degrees of focus. That is, when theaerial image is defocused from optimum, the dimensions of the unexposedarea within a latent image and the resist shape, and the latent imageand resist space, will both either increase or decrease in dimension, orremain the same.

Focus and exposure dose parameters may be determined as a mathematicalfunction of the measured dimensions of the latent or developed imageshape and space. It has been found that by taking the difference and sumof complementary tone line-length or other dimensions of the latentimage or resist pattern, the effect of exposure dose and focus variationcan be determined. Specifically, by taking the difference of a dimensionof the complementary latent image shapes and spaces, or, preferably, thecomplementary resist shapes and resist spaces, the effect of exposuredose can be determined. By taking the sum of the dimensions of thecomplementary latent image shape and space, or, preferably, the resistshape and resist space, the variation in focus can be determined.

In each case, actual measurements are made of the correspondingdimensions of the latent image shape and space, or the resist imageshape and space, on the substrate. These measured dimensions arecompared with each other for the same or corresponding dimension. Forexample, in comparing the complementary patterns of the latent image orresist images in FIG. 7, L₁ will be compared to L_(s), and W₁ will becompared to W_(s). In order to facilitate comparison, the nominalcomplementary dimensions in the shapes and spaces to be measured shouldbe identical or some known relationship to each other, as established bytheir nominal values. For example, under ideal exposure and focusconditions, L₁ equals a×L_(s), and W₁ equals b×W_(s). Likewise, incomparing the complementary patterns of the latent image or resistimages in FIG. 8, L₁ will be compared to L_(s).

Ideally, in the case of measuring exposure dose, the difference betweenthe measured dimensions of the latent image or the resist shape, on onehand, and the measured dimensions of the latent image space or theresist space, on the other hand, will be a predetermined target value.This target value may be any value, positive, negative or zero. Forexample, where the dimensions of the shape and space on the mask areequal (or nearly equal), the target value of the difference of theresist shape and space could be zero. An acceptable tolerance about thetarget value may be determined by experimentation to mark the regimeover which exposure dose variation is acceptable. However, for adifference in measured dimension outside that predetermined tolerance,one would then change the exposure dose in order to correct thevariation in the dimensions between the latent image or resist shape andthe unexposed area within a latent image or resist space.

In the case of controlling focus variation, the sum of the selecteddimension of the shape and space are considered, and a target value isdetermined. For example, where the dimensions of the shape and space onthe mask are equal, ideally the sum of the measured correspondingdimension of the latent image of the resist shape and resist space couldbe twice the dimensions of the nominal dimension of the shape or spaceunder perfect focus conditions. In this example, if one were to subtractfrom the sum of the measured dimensions of the latent image or resistshape and the latent image or resist space twice the nominal dimension,the target value could be zero. However, an acceptable tolerance aboutthe target value may be determined by experimentation to be acceptablefor focus variations. If this determined value is outside thepredetermined tolerance, then steps may be taken to modify or change thefocus of the aerial image on the resist film.

It has also been found that measurement of line lengths and inparticular, measurement of the distance between tapered ends of a resistshape or space are more sensitive to dose and focus variations than thewidths of the resist shapes or spaces. This indicates that measurementsof lengths of complementary shapes such as latent image or resist shape122a and latent image or resist space 126a (FIG. 8) having tapered endswould tend to determine changes in length with exposure and focus moreprecisely.

FIGS. 9-16 depict simulations of response to measurement of selectedcorresponding dimensions on complementary tone patterns. The units ofdimension and focus are in microns, and the legend for the plottedpoints is the unitless ratio of exposure dose/dose to clear (i.e., thedose required to clear an unpatterned area on the substrate). FIGS. 9and 10 show the measurement of line (shape) widths and space widths,respectively, of complementary resist shapes and spaces of the typeshown in FIG. 7 as a function of focus, where the nominal width W₁equals the nominal width W_(s) equals 0.3 microns. FIGS. 11 and 12 showthe difference and sum, respectively, of the above complementary resistshape and space width dimensions as a function of focus.

FIGS. 13 and 14 show the measurement of line (shape) lengths and spacelengths, respectively, of complementary resist shapes and spaces of thetype shown in FIG. 7 as a function of focus, where the nominal length L₁equals the nominal length L_(s) equals 1 micron. FIGS. 15 and 16 showthe difference and sum, respectively, of the above complementary resistshape and space length dimensions as a function of focus.

Accordingly, in controlling focus or exposure dose parameters in thelithographic process, the steps to be taken are preferably as follows:

1) Providing a substrate on which is deposited a layer of resistmaterial having a resist threshold.

2) Illuminating and exposing onto the resist a complementary tonepattern having a shape which corresponds to an area on the resist filmhaving an exposure dose below the resist threshold a space whichcorresponds to an area on the resist film having an exposure dose abovethe resist threshold. The shape and space have corresponding dimensionswhich have a known relationship to each other.

3) Creating on the resist film latent images of the complementary toneshape and space and, optionally, developing the latent image shape andspace.

4) Measuring the corresponding dimensions on the latent or developedimage shape and space.

5) Determining the adequacy of focus or exposure dose parameters as afunction of the measured dimensions of the latent or developed imageshape and space.

Additionally, it is advantageous to create an exposure/focus matrix ofthe type shown in FIGS. 9-16 which maps measured line and space widthsand measured line and lengths, along with the sum and difference ofthese widths and lengths, as a function of focus and exposureparameters. When it becomes necessary to adjust focus or exposure doseon a product substrate, these relationships can be used to calibrate theadjustment of the exposure and/or focus parameters.

It has also been determined that the results of lithographic patternetching can also be found to differ depending on the sum or differenceof dimensions in complementary etched patterns. That is, the dimensionsof etched shapes or etched spaces change in opposite directions withetching time and rate whereas only more fundamental changes in theetching process will cause them to vary in the same direction. Thesefundamental etch process changes include effects that deposit etchmaterials on the sidewalls, and what is typically characterized in theart as "polymerization".

For example, after etching the resist shapes and spaces shown in FIG. 7,the raised etches images 222 and 224 are shown in FIG. 17 remaining onthe base 82 of the substrate. "Shape" when used in connection with anetched image refers to an area of an etched image which has not beenremoved from the substrate and is bounded by an area from whichsubstrate material has been removed. Shapes can also be referred to aslines. "Space" when used in connection with an etched image refers to anarea of an etched image which has been removed from the substrate and isbounded by an area from which substrate material has not been removed.Spaces can also be referred to as trenches. Etched image shape 222corresponds to resist shape 122, and etched image space 226 correspondsto resist space 126. The width and length of the etched shape 222 are W₁and L₁, respectively. The width and length of the etched space 226 areW_(s) and L_(s), respectively. Likewise, in FIG. 17 there is shown theraised etched images 222a and 224a which remain after etching thecorresponding resist images in FIG. 7. The length of the etched shape222a is L₁ and the length of the etched space 226a is L_(s).

Etch time and other etching parameters sensitive to the differentialetch rate of the different tone patterns may also be determined as amathematical function of the measured dimensions of the etched imageshape and space. By taking the sum and difference of complementary toneline length pattern dimensions in the etched pattern shapes and spaces,the effects of etch time and rate variation can be segregated from morefundamental changes in the etch process. Specifically, by taking thedifference in the dimensions of the etched shapes and etched spaces, theeffect of etch time and rate variations can be determined. By taking thesum of the measured dimensions of the etched shapes and etched spaces,other and more fundamental changes in the etched process can bedetermined, such as a change in the differential etch rate of thedifferent tone patterns. The use of measurable complementary toneline-length pattern on product wafers, enables the implementation of apatterning control system where exposure dose and etched time/ratevariations can be corrected, and detrimental changes in focus and etchconditions can be determined.

As with measurement of latent image or resist shapes and spaces, actualmeasurements are made of the corresponding dimensions of the etchedimage shape and space on the substrate base. These measured dimensionsare compared to with each other for the same or corresponding dimension.For example, in comparing the complementary patterns of the etched imageor resist images in FIG. 17, L₁ will be compared to L_(s), and W₁ willbe compared to W_(s). In order to facilitate comparison, the nominalcomplementary dimensions in the shapes and spaces to be measured shouldbe identical or some known relationship to each other, as established bytheir nominal values. For example, under ideal exposure and focusconditions, L₁ equals c×L_(s), and W₁ equals d×W_(s). Likewise, incomparing the complementary patterns of the etched image or resistimages in FIG. 18, L₁ will be compared to L_(s).

Under ideal conditions, the difference between the measured dimensionsof the etched image shape and the measured dimensions of the etchedimage space will be a predetermined target value. This target value maybe any value, positive, negative or zero. For example, where thedimensions of the resist image shape and space are equal (or nearlyequal), the target value of the difference of the etched image shape andspace could be zero. An acceptable tolerance about the target value maybe determined by experimentation to mark the point at which etch timeand rate variations is acceptable. However, for a difference in measureddimension outside that predetermined tolerance, one would then changethe etch time and rate in order to correct the variation in thedimensions between the etched image shape and the etched image space.

In the case of controlling other etch process parameters, such as thedifferential etch rate of the different tone patterns, the sum of theselected dimension of the shape and space are considered, and a targetvalue is determined. For example, where the dimensions of the shape andspace on the resist are equal, the sum of the measured correspondingdimension of the etched image shape and etched image space could betwice the dimensions of the nominal dimension of the shape or spaceunder perfect etch process conditions. In this example, if one were tosubtract from the sum of the measured dimensions of the etched imageshape and the etched image space twice the nominal dimension, the targetvalue could be zero. However, an acceptable tolerance about the targetvalue may be determined by experimentation to be acceptable for otheretch process variations. If this determined value is outside thepredetermined tolerance, then steps may be taken to modify or change theother etch process parameters.

To control time and other etching parameters in the process, the stepsto be taken are preferably as follows:

1) Providing a substrate having an overlying resist film layer with acomplementary tone developed image pattern having a developed imageshape made of the resist film and a developed image space removed fromthe resist film. The developed image shape and space have correspondingdimensions.

2) Contacting the developed image shape and space with an etchant for adesired time to create an etched image of the developed image shape andan etched image of said developed image space on said substrate.

3) Measuring the corresponding dimensions on the etched image shape andspace.

4) Determining time or other etching parameters as a function of themeasured dimensions of the etched image shape and space.

As with the exposure/focus adjustment, it is advantageous to create anetching time matrix of the type shown in FIGS. 9-16 for exposure andfocus which maps measured line and space widths and measured line andlengths, along with the sum and difference of these widths and lengths,as a function of etching time and other etching parameters. When itbecomes necessary to etching time and other etching parameters on aproduct substrate, these relationships can be used to calibrate theadjustment of the respective parameters.

The preferred decision making flow chart for practice of the presentinvention is shown in FIG. 19. Initially, in step 102 the mask patternsare prepared and exposed as described previously with complementaryopaque shapes and transparent spaces, in this example being of equaldimension. If the latent image shapes and spaces are to be measured, theprocess proceeds directly to the next step. If the resist image shapesand spaces are to be measured, the latent images are developed. In steps304 and 306, the latent image or resist shapes and spaces arerespectively measured. The sum and difference of the measurement of thelatent image or resist shapes and spaces is determined in step 308. Incomparing the difference in step 310, if the difference is outside apredetermined tolerance about the target value, the exposure portion ofthe process is deemed to fail and the exposure dose is adjusted, 312.After adjustment, the complementary mask pattern is again exposed, 302,and remeasured as before. If the difference in step 310 is within thetolerance about the target value, the exposure dose process is passed onto the next step, etching the pattern, 318.

After step 308, the sum of the measurements of the latent image orresist shapes and spaces are made, and twice the nominal dimension issubtracted. In comparing this value in step 314, if the value is outsidea predetermined tolerance about the target value, the focus portion ofthe process is deemed to fail and the focus dose is adjusted, 316. Afteradjustment, the complementary mask pattern is again exposed, 302, andremeasured as before. If the value in step 314 is within the toleranceabout the target value, the focus process is passed on to step 118,etching the pattern.

The complementary pattern is etched and the etched shapes and spaces aremeasured in steps 320 and 322, respectively. The sum and difference ofthe measurement of the etched shapes and spaces is determined in step324. In comparing the difference in step 326, if the difference isoutside a predetermined tolerance about the target value, the etch timeand rate portion of the process is deemed to fail and the time and rateare adjusted, 328. After adjustment, the complementary resist pattern isagain etched, 318, and remeasured as before. If the difference in step326 is within the tolerance about the target value, the etch time andrate process is passed and this portion of the process is deemedcomplete.

After step 324, the sum of the measurements of the etched image shapesand spaces are made, and twice the nominal dimension is subtracted. Incomparing this value in step 330, if the value is outside apredetermined tolerance about the target value, other portions of theetch process are deemed to fail and the other portions are adjusted,332. After adjustment, the complementary resist pattern is again etched,318, and remeasured as before. If the difference in step 330 is withinthe tolerance about the target value, the other portions of the etchprocess are deemed complete.

In the above description of the processes of the present invention forfirst controlling lithographic parameters (focus and exposureparameters) and then etching parameters (time and other parameters), thelithographic parameters have been corrected to obtain a resist shape andspace of a desired tolerance prior to commencing etching. It is alsopossible to use the etching process to correct or compensate forexcessive tolerances in the lithographic tolerances. For example, if itwere determined that the exposure parameter in the lithographic processwas outside the predetermined tolerance, rather than correcting theexposure parameter directly, a compensation may be made in the etchingprocess to overcome the defect in the exposure. In this manner,knowledge of the nature of the lithographic problem may be employed tomake the correction in the subsequent etching step, rather thanrepeating the lithographic processing to correct the problem.

Preferably, the dimensions of the shapes and spaces of thelatent/developed images and etched images are larger than the resolutionof the metrology tool employed. The minimum dimensions employed, such asfor the width of isolated or nested lines or trenches (whensignificantly less than the lengths of the lines or trenches), may be onthe order of the minimum feature size of the circuit pattern.

By following the aforementioned methods, the present invention providesa test pattern and evaluation method for determining exposure and focusconditions, as well as a test pattern and evaluation method fordetermining etching time and rate conditions and other etching processconditions. For each method, one pattern group is capable ofdistinguishing between either exposure and focus problems, or betweenetching time and rate problems and other etching process problems insemiconductor pattern processing. The present invention may be used withexisting metrology instruments and exposure and etching equipment, and,further, is easy and inexpensive to utilize.

Even for the simulated examples shown in FIGS. 11, 12 and 15, 16, it hasbeen found that the difference and sum of the shape and space dimensionsdo not completely separate the dose and focus dependence over the entiredose and focus regime. The difference plots in FIGS. 11 and 15 showincreasing focus dependence as the dose deviates from an "isofocal"value at which the difference dimension is independent of focus. The sumplots in FIGS. 12 and 16 show some separation of the curves withchanging dose, particularly at extremes of defocus.

In practice, the behavior of spaces and shapes with exposure dose andfocus may follow even more dissimilar curves than those of the simulatedexamples. Observed differences in the relative sensitivity to dose andfocus, and even in the position of optimum focus, of nominally identicalspaces and shapes can be ascribed to the non linear characteristics ofthe lithography and etch process. Some examples of specific contributingfactors are:

1. For a given pattern level it may be desirable to operate in anoverexposed or underexposed condition relative to the dose conditionthat replicates the mask dimension. This can shift the dose operatingpoint to a region of the focus-exposure plane where spaces and shapeshave different sensitivity to dose variation.

2. Characteristics of the mask, such as the relative size or cornerrounding attributes of spaces and shapes, can cause differences in theirdose and defocus sensitivity.

3. Characteristics of the resist, such as contrast and exposurelatitude.

4. Characteristics of the aerial image produced by the exposure tool,such as flare.

5. Characteristics of the etch process, such as sensitivity to localpattern density.

Under conditions where the shapes and spaces exhibit significantlydifferent sensitivities, a more sophisticated approach to the separationof dose, focus and etch variables may be required than a simple sum anddifference of the respective dimensions.

A flowchart of an improved feature size control system using tonereversed patterns is shown in FIG. 20, which is directed to the exposuredose and focus characteristics of the lithography. The process is firstcharacterized by printing a complementary tone reversing pattern under aseries of different exposure and focus conditions 350. For each (E_(i),Z_(j)) combination, the shape (A_(ii)) and space (B_(ii)) dimensions aremeasured, 352. The target values (A_(to) B_(to)) are determined bycorrelation to the desired dimensions of the circuit pattern (box 354).At the optimum focus Z₀ determined as the point at which the rate ofchange of A and B with z is minimum, the target values must correspondto a single value of dose, E_(i).

In box 356, the dependence of the shape and space dimensions on dose andfocus in the neighborhood of the target values (A_(to), B_(to) andE_(t), z_(o)) are modeled by a set of parametric equations:

    α=ƒ(ε,ζ,a.sub.1,a.sub.2 . . . )

    β=ƒ(ε,ζ,b.sub.1,b.sub.2, . . . )(1)

where α, β, ε and ζ are defined as deviations from the target values:

    α=A-A.sub.to, β=B-B.sub.to ε=E-E.sub.t and ζ=z-z.sub.o.

For examples, the equations:

    α=a.sub.1 ζ.sup.2 +a.sub.2 ε

    β=b.sub.1 ζ.sup.2 +b.sub.2 ε             (2)

are used to capture the case where the exposure dose sensitivity(represented by slope parameters a₂, b₂) and defocus sensitivity(represented by curvature parameters a₁, b₁) differ between the shapeand space patterns. The parameters (a₁, a₂, . . . ) and (b₁, b₂, . . . )may be determined by a conventional least-squares fit to the measureddose-focus data.

Once the parameters have been established by fit to the model, the setof equations (1) can be used to solve (box 358) for the dependence ofdose and focus on the shape and space dimensions:

    ε=g(α, β, a.sub.1 . . . a.sub.n, b.sub.1 . . . b.sub.n)(3)

    ζ=h(α, β, a.sub.1 . . . a.sub.n, b.sub.1 . . . b.sub.n)(4)

For the example given by equation (2), equations (3) and (4) can beexpressed analytically as:

    ε=(b.sub.1 α-a.sub.1 β)/(a.sub.2 b.sub.1 +a.sub.1 b.sub.2)                                                  (5)

    ζ.sup.2 =(b.sub.2 α+a.sub.2 β)/(a.sub.2 b.sub.1 +a.sub.1 b.sub.2)                                                  (6)

For more complex models (1) than the example (2), an analytic solutionmay not be possible and numerical methods must be employed to solve forε and ζ, In the simpler case where the dose and focus sensitivity ofshapes and spaces are identical, namely b₁ =a₁, and b₂ =a₂, thenequations (5) and (6) reduce to the simple sum and differenceexpressions:

    ε=(α-β)/(2a.sub.2)                      (7)

    ζ.sup.2 =(α=β)/(2a.sub.1)                  (8)

The underlying physics of the shape and space dependence on dose andfocus dictates that the more sophisticated expressions for dose andfocus deviation in Equations (3) and (4), will behave as modificationsto the simple sum and difference expressions in Equations (7) and (8).Thus, the sum and difference paths of the control system shown in FIG.19 may be most generally described as the "modified" sum and differenceof the shape and space dimensions.

The above describes the setup method by which operating conditions of afeatures size control system can be established using tone-reversedpatterns. This method may be used in the in-line implementation of thecontrol system in manufacturing as follows.

The target dose and focus (E_(t), z_(o)) determined in the setupprocedure can be used to initiate the manufacturing process. Over time,the corrections required to keep product within the required dimensiontolerances may cause deviations from the original target values, suchthat the estimated dose and focus for the (i)^(th) product lot is(E_(i), z_(i)) as shown on the right side of FIG. 20. Each productionlot will have on a substrate, one or more complementary tone-reversedpatterns as described previously. After exposing the lot at (E_(i),z_(i)) (box 362) and measuring the shape and space of the pattern (box364), the deviation of the tone-reversed measure values (A_(i), B_(i))(box 368) from their respective target values (A_(to), B_(to)) can besubstituted in the predetermined equations (3) and (4) to compute theequivalent dose and focus deviations (ε_(i), ζ_(I)) (box 372). Were theexposure of the i^(th) lot to be repeated, the settings (E_(i) -ε_(i),z_(i-) ζ_(I)) would guarantee the target dimensions (A_(to),B_(to)). Inpractice, however, it is of more value to predict the settings to beused on the (i+1)^(th) lot. In a continuously running manufacturingline, the dose can be forecast based on the variation of the last Nlots. Depending on the continuity of product flow and the stability ofthe process, an appropriate forecasting algorithm can be derived, forexample, a rolling average: ##EQU1##

The new setting is then fed back (box 374) to the next lot of substratesto be processed (box 380), and a correction to the focus (box 376) orexposure dose (box 378) is made if needed.

Since the variation of dimension is usually symmetric with defocus,there is likely to be ambiguity regarding the sign of the focuscorrection. Nonetheless, a statistical check of the focus deviation bythe equation:

    |ζ|>μ.sub.|ζ| +3σ.sub.|ζ|                  (10)

may be used to determine if a significant focus shift has occurred on aspecific lot; where |ζ₁ | is the absolute value of the computed focusshift on the i^(th) lot, μ.sub.|ζ| is the mean of the absolute value ofthe focus shift over many lots, and σ.sub.|ζ| is the standard deviation.Since significant focus shifts are believed to be rare, it is sufficientto be able to signal when one has occurred and to determine the sign ofthe correction by the conventional technique of measuring a productwafer on which focus has been intentionally varied.

A method analogous to that described above and in FIG. 20 may be used tocontrol etching and other parameters by complementary tone developedimage patterns on a resist film layer on a substrate. As shown in FIG.21, the process is first characterized by etching a complementary tonereversing pattern under a series of different etch time conditions (box380). For each T_(i) condition, the shape (A_(i)) and space (B_(i))dimensions are measured, box 382. The target values (A_(o), B_(o))corresponding to etch time T_(o) are determined by correlation to thedesired dimensions of the circuit pattern (box 384). At the optimum etchtime T₀ determined as the point at which the rate of change of A and Bwith T is minimum, the target values must correspond to a single valueof dose, T_(i).

In box 386, the dependence of the shape and space dimensions on etchtime in the neighborhood of the target values (A_(o), B_(o) and T_(o))are modeled by a set of parametric equations:

    α=ƒ.sub.e (τ,a.sub.1,a.sub.2 . . .)

    β=ƒ.sub.e (τ,b.sub.1,b.sub.2, . . . )    (1a)

where α, β, and τ are defined as deviations from the target values:

α=A-A_(o) (shape dimension)

β=B-B_(o) (space dimension)

τ=T-T₀ (etch time)

For examples, the equations:

    α=a.sub.1 τ

    β=b.sub.1 τ                                       (2a)

are used to capture the case where the etch sensitivity (represented byslope parameters a₁, b₁) differ between the shape and space patterns.The parameters a₁ and b₁ may be determined by conventional methods tothe measured etch condition data.

Once the parameters have been established by fit to the model, the setof equations (1a) can be used to solve (box 388) for the dependence ofdose and focus on the shape and space dimensions:

    τ.sup.α =g(α, a.sub.1 . . . a.sub.n)       (3a)

    τ.sup.β =h(β, b.sub.1 . . . b.sub.n)         (4a)

For the example given by equation (2a), equations (3a) and (4a) can beexpressed analytically as:

    τ=τ.sup.α =τ.sup.β =α/a.sub.1 =α/b.sub.1 (5a)

By measuring A and B, redundant determinations are made of the etch timedeviations (τ.sup.α,τ.sup.β), which should be equal. If in practice theyare found to differ by a statistically significant amount, there wouldbe indicated a change in fundamental etch properties. Statisticalprocess control methodology can be applied to τ.sup.α -τ.sup.β =δτ todetermine whether a significant process shift has occurred.

The target etch time (T_(o)) determined in the setup procedure can beused to initiate the manufacturing process. Over time, the correctionsrequired to keep product within the required dimension tolerances maycause deviations from the original target values, such that theestimated etch condition for the (i)^(th) product lot is (T_(i)) asshown on the right side of FIG. 21. Each production lot will have on asubstrate one or more complementary tone-reversed patterns as describedpreviously. After etching the lot at (T_(i)) (box 392) and measuring theshape and space of the pattern (box 394), the deviation of thetone-reversed measure values (A_(i), B_(i)) (box 368) from theirrespective target values (A_(o), B_(o)) can be substituted in thepredetermined equations (3a) and (4a) to compute the equivalent etchdeviation (τ_(i)) (box 402). Were the exposure of the i^(th) lot to berepeated, the settings (T_(i) -τ_(i)) would guarantee the targetdimensions (A_(o),B_(o)). In practice, however, it is of more value topredict the settings to be used on the (i+1)^(th) lot. In a continuouslyrunning manufacturing line, the etch time and condition can be forecastbased on the variation of the last N lots. Depending on the continuityof product flow and the stability of the process, an appropriateforecasting algorithm can be derived, for example, a rolling average:##EQU2##

The new setting is then fed back (box 404) to the next lot of substratesto be processed (box 390), and a correction to the etch time (box 408)or etch diagnostics and re-setup (box 406) is made if needed.

The improved metrology target of the present invention uses aself-consistent design to transcend the limitations of opticalmicroscopy. The target employs measurement of array edges instead ofindividual pattern elements, as discussed above.

Preferably, there is employed to provide in-line measurement of thetargets of the present invention the optical imaging tool and system asdisclosed in copending U.S. application Ser. No. 08/643,138 and U.S.application Ser. No. 08/919,993 entitled Optical Metrology Tool AndMethod of Using Same (filed on even date herewith), assigned to theassignee of the present invention, the disclosures of which are herebyincorporated by reference. Such targets on a substrate wafer consist inpart of an array of parallel pattern elements or lines of length atpitch P. The pitch is matched to the minimum pitch in the chip designfor a specific masking layer. The array width, W_(o), is large relativeto the minimum resolution of the metrology tool. For the particularpattern design shown, W_(o) also corresponds to the length of theindividual pattern elements. If P is below the optical resolution:

    P<λ/(NA(1+σ))                                 (11)

wherein the wavelength of the light is λ, the optical metrology toolnumerical aperture is NA and partial coherence is σ, then the opticalimage of the array will be a featureless wide line as shown, wherein thepattern elements are unresolved in the direction of the pitch, but wellresolved in the direction of the array width. Using optical microscopyin which the array pitch, numerical aperture, coherence and lightwavelength are selected so that the array elements are unresolved, theimage of the featureless line may be brought into focus and edgedetection may be conducted by applying algorithms by a variety ofwell-known techniques to determine the measured width of the array

A consequence of using such a target design, in which the minimum pitchis perpendicular to the measurement direction, is that the length ofminimum dimension patterns is monitored, rather than their width. Linelengths tend to be significantly more sensitive to process conditionsthan line widths as the resolution limits of any given lithographyprocess are approached.

An added benefit to having the target pitch perpendicular to themeasurement direction is that it alleviates the need to satisfy equation11, namely, to keep the pitch below the optical microscope resolution.The result of partially or even fully resolving the pattern elements isthat the pixels along the edge of the array see a modulation in the edgeposition. However, on average over along length of the array this stillresults in a single edge position sensitive primarily to the length ofthe individual lines. Nonetheless, the edge acuity of the detectedintensity is decreased when the lines are resolved, thus degrading theprecision of the measurement. To optimize this metrology approach forsemiconductor manufacturing applications, the configuration of theimproved optical microscope of the present invention preferably insuresthat Equation 11 is met for the targets employed, such as thosedescribed above.

The target configurations can be tailored to mimic pattern layers in themanufacturing process (e.g., lines, contacts or islands), to increasethe sensitivity of metrology (e.g., using tapered lines, daggers orsub-resolution patterns), and to characterize specific attributes of thelithographic process (e.g., linearity and proximity bias). The targetenables optical measurement of critical dimension variation of bothtones for patterning process control.

A first target is depicted in FIGS. 22a and 22b. The transition betweena contrasting target area or island on the left) and a surrounding cleararea on a substrate defines an edge 141 of an arbitrary pattern shape(FIG. 22a). The straight edge of target area 140 may be transformed to ameasurable pattern by creating a serpentine edge 142 as shown in FIG.22b. Edge 142 is created by contacting a similarly contrasting array ofspaced individual elements 143 with edge 141 of target 140'. Eachelement 143 has length and width, with the ends of the array beingformed along parallel lines (perpendicular to the length of the elements143) forming the array edge 141, 142. The spacing (clear area) betweenindividual elements equals the element width. The array width W is equalto the length of the elements or lines 143, and the array length L isequal to the distance between opposite far edges of the first and lastof the elements 143.

Measurement of the pattern in FIG. 22b can be achieved using variousmetrology techniques (such as optical microscopy, scanning electronmicroscopy and atomic force microscopy) provided a detectable edgeexists between the serpentine area and the surrounding clear areas. Asshown in FIGS. 23a, a target 145 has contrasting area 144 with straightedge 146 contacting the edge of an array made up of spaced parallellines 147. The ends of lines 147 opposite area 144 form serpentine edge148. To measure target 145, the individual elements of the serpentineneed not be well resolved. In particular, an optically measurablecomplementary tone pattern can be created from this serpentine edge asshown in FIG. 23b by not resolving the individual elements, whereoptical contrast is observed on both the line and space (144) sides ofpattern 145. The dimensions of the pattern (W_(is), and L_(is)) arefocus sensitive, whereas the center of position of the pattern (X,Y) isexposure sensitive, where x is the center of array width W_(is) and y isthe center of array length L_(is).

Various compact and measurable patterns can be constructed from thebasic pattern of FIGS. 22b and 23a. In FIG. 24 there is shown atone-reversing target 150 having serpentine edge 153 made using lines152 which taper from a width at edge 154 of contrasting area 151 down toa point at opposite array edge 153. In practice, the individual elementsof the serpentine are formed by stepping the pattern in increments ofthe minimum design grid (typically 25 nm). A symmetrical stepping can beused for lines 152a, as shown in FIG. 24a, or a single-sided steppingcan be used for lines 152b, as shown in FIG. 24b. The single steppinghas the advantage that a more gradual taper is possible.

A target improvement using tone reversing arrays is shown in FIG. 25.Target 170 comprises a pair of mirror-image arrays 171, 173 ofequilength parallel elements or lines (shapes) 175 in contact with andon opposite sides of a rectangular area or island (shape) 172 of thesame nominal length, width and tone as arrays 171, 173. Both the lines175 and island 172 contrast with the substrate. The location of the freeedge of array 171 is shown as x₁, the location of the free edge of array173 is shown as x₄, the location of the common edge between array 171and island 172 is shown as x₂, and the location of the common edgebetween array 173 and island 172 is shown as x₃. The width of arrays171, 173 and island 172 is given by ^(i) W_(o). Spaced from array 173 bya distance ^(i) S_(o) (nominally equal to the length of lines 175, 179)is array 177, comprising equilength parallel lines 179, in contact alongan array edge with rectangular island 178 of similar nominal length andwidth. The location of the free edge of array 177 is shown as x₅, andthe location of the common edge between array 177 and island 178 isshown as x₆.

The expression of bias and pitch as a function of the island and spaceedge locations enables the separation of CD response to exposure doseand/or etch time from CD response to other process variables, such asfocus, film thicknesses, and substrate properties. For example, anisland-to-space bias ^(is) B_(m) and pitches ^(P) W_(m), ^(P) S_(m) canbe determined by the following equations:

    .sup.is B.sub.m =.sup.i W.sub.m -.sup.S W.sub.m3 =.sup.s S.sub.m -.sup.i S.sub.m                                                   (12)

    .sup.P W.sub.m =.sup.i W.sub.m +.sup.s W.sub.m             (13)

    .sup.P S.sub.m =.sup.i S.sub.m +.sup.s S.sub.m             (14)

Since the island (shape) and space edges move in opposite directionswith exposure dose, but in the same direction with defocus, ^(is) B_(m)is primarily sensitive to dose and insensitive to defocus, and pitches^(P) W_(m), ^(P) S_(m) are primarily sensitive to defocus andinsensitive to dose. The ability to distinguish dose and defocusdependence of CD is a key attribute of the tone reversal target.

If the island (shape) and space patterns have similar contrast whenimaged in an optical microscope (for example, they are both dark withrespect to the surrounding background), then changes to the perceivededge location with substrate properties will affect them approximatelyequally. Consequently, the dose dependent ^(is) B_(m), expressed as adifference between the two pattern widths, will be relativelyinsensitive to variations in the optical properties of the substrate.Because dose is the principal control parameter for CD, the ability tosuppress false sensitivity to substrate properties is a second keyattribute of the tone reversal target.

The preferred target may be specified by its internal pitch, P, and byits array width W. There should be adequate image contrast between thetarget and its surrounding area. Image contrast is a function of thewavelength and partial coherence tool parameters, and the opticalproperties of the patterned target, the adjacent unpatterned area andthe underlying substrate. At different wavelengths, the patterned areacan be brighter or darker than the surrounding area, and the bandwidthof the high contrast regions tends to be on the order of 25-50 nm. Inthe target depicted in FIG. 25, the contrast is determined principallyby the relative reflectivity of the target and its surroundings.

For the tone reversing target, changes in target size or dimension ofelements may be observed as changes in target position. This enables themeasurement of critical dimension using an optical overlay metrologytool or optical alignment system. In the case of overlay or alignmentmetrology, it would be necessary to detect centerline shifts on atarget, namely, the relative change of any pair of edge positions thatdefine the target. In the target variations depicted in FIG. 25, bothcan be characterized by six types of centerlines C between edge pairs:##EQU3##

The edge orientation may be defined as the direction between patternedand unpatterned regions of the target. C₁, C₄ are the centerlinesbetween edges of opposite tone oriented in opposite directions, and willbe primarily sensitive to change in exposure dose (when exposing atarget on a resist film) or etch time (when etching a developed targeton a resist film). C₂, C₅ are the centerlines between edges of oppositetone oriented in the same direction, and will be primarily sensitive tochange in focus (when exposing a target on a resist film) or sensitiveto the differential etch rate of the different tone patterns (whenetching a developed target on a resist film). C₃, C₆ are the centerlinesbetween edges of the same tone oriented in the same or oppositedirections. Since both edges have the same sensitivity to feature size,it will be independent of exposure dose or focus (when exposing a targeton a resist film) or etch parameters (when etching a developed target ona resist film). Consequently, C₃, C₆ may be used for conventionaloverlay or alignment measurement.

In FIGS. 26a, 26b there are shown complementary measurement targets 240,242, respectively. Targets 240, 242 are the exact tone opposites of eachother. On each target 240, 242 there may be measured lines/space lengthmetrology dimensions (L_(i), L_(s) and L_(is)) and pattern pitchmonitoring dimensions (P_(i), P_(s) and P_(is)) as shown with respect tothe array edges. Pitches indicated can be measured along with patterndimensions to monitor precision, cull bad measurements and/or determinepattern type with a pitch encoded target or label, as described incopending U.S. application Ser. No. 08/727,138 filed Oct. 8, 1996, thedisclosure of which is hereby incorporated by reference. It may be notedthat only one tone-reversing edge is present (L_(is)) in targets 240,242.

Complementary measurement targets 244, 246 for optical line/space lengthmetrology (L_(i), L_(s) and L_(is)) and pattern pitch monitoring (P_(i),P_(s) and P_(is)) are depicted in FIGS. 27a, 27b, respectively, wherethe line/space metrology and pitch structures overlap. In targets 244,246, there are present three tone-reversing edges (L_(is)). FIGS. 28a,28b show target 244', 246' similar to the respective targets in FIGS.27a, 27b, except that tapered lines are used to form the arrays.

In the targets depicted in FIGS. 22a through 28b, measurements within agiven target can be obtained in a single optical scan, as alternativesto the target of FIG. 25.

FIGS. 29-36 depict optical measurements made on the target depicted inFIG. 25. Target dimension in units of microns are plotted againstdefocus in microns, and the legend for the plotted points is dose inunits of millijoules/cm². The measurements are made on a target as shownin FIG. 25 where lines 175, 179 have a width of 0.275 microns and aspacing between lines of 0.275 microns. FIGS. 29-32 show examples of acomplementary tone reversing target exposed and developed on a resistlayer in which shape and space exhibit similar exposure sensitivity anddefocus curvature. The A=x₃ -x₂ and B=x₅ -x₄ dimensions are nominallyidentical on the masks used to project the target images on the resistfilm, and these dimensions on the targets form corresponding imagespaces and shapes. Dimension A plotted vertically in FIG. 29 indicatesthe shape length separation relative to nominal. Dimension B plottedvertically in FIG. 30 indicates the space length separation relative tonominal. FIG. 31 is a plot of (A+B)/2 and FIG. 32 is a plot of (B-A)/2.

FIGS. 33-36 show examples of a target exposed and developed on a resistlayer in which shape and space have significantly different exposuresensitivity and defocus curvature. In this case, dimension B plotted inFIG. 33 is the distance x₆ -x₃ in FIG. 25 indicates the measured spacelength. Dimension A plotted vertically in FIG. 34 is the distance x₄ -x₁in FIG. 25, and indicates the measured shape length. FIG. 35 is a plotof (A-B)/2 and FIG. 36 is a plot of (A+B)/2. The case shown in FIGS.34-37 is preferably analyzed by the method and system depicted FIG. 20to cleanly separate dose and focus dependence.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

Thus, having described the invention, what is claimed is:
 1. A processfor controlling etching or other parameters in a lithographic processcomprising the steps of:a) providing a plurality of a first set ofcomplementary tone developed image patterns on a resist film layer on asubstrate, each of said first set of complementary tone patternscomprising: i) a first pattern portion having a developed image shapemade of said resist film and ii) a second pattern portion having adeveloped image space removed from said resist film, said shape andspace having corresponding dimensions; b) etching each of said developedfirst set of complementary tone patterns under different etchingconditions to create an etched image of said developed image shape andan etched image of said developed image space; c) measuring thedimensions of the etched image shapes and spaces on each of said exposedfirst set of complementary tone patterns; d) determining optimum etchingor other conditions based on the measurements of step (c); e)determining the dependence of etching or other conditions on saiddimensions of the image shapes and spaces near the optimum etching orother conditions determined in step (d); f) providing one or more of asecond set of complementary tone developed image patterns on a resistfilm layer on a substrate, each of said second set of complementary tonepatterns comprising: i) a first pattern portion having a developed imageshape made of said resist film and ii) a second pattern portion having adeveloped image space removed from said resist film, said shape andspace having corresponding dimensions; g) measuring said dimensions ofthe etched image shapes and spaces on each of said exposed second set ofcomplementary tone patterns; and h) determining adequacy of etching orother parameters on each of said exposed second set of complementarytone patterns based on the measurements and determinations of steps(a)-(e).
 2. The process of claim 1 further including the step of:i)establishing etching or other parameters for subsequent etching of athird set of complementary tone patterns by applying a measurement ofsaid dimensions of image shapes and spaces on at least one of saidetched second set of complementary tone patterns to the dependence ofetching or other conditions made in step (e).
 3. The process of claim 1further including the step of:i) establishing etching or otherparameters for subsequent etching of a third set of complementary tonepatterns by applying a measurement of said dimensions of image shapesand spaces on at least one of said etched second set of complementarytone patterns to the dependence of etching or other conditions made instep (e) to predict a new etching or other parameter, and taking anaverage of the predicted new etching or other parameter and the etchingor other parameter of said at least one of said etched second set ofcomplementary tone patterns.
 4. The process of claim 1 wherein thedimensions of said shape and space are nominally identical, and whereinthe adequacy of etching or other parameters are determined based on thedimensions on said image shape and space.
 5. The process of claim 1wherein said shape and space are rectangular having a width and alength, and wherein the adequacy of etching or other parameters aredetermined based on the width or length dimensions on said image shapeand space.
 6. The process of claim 5 wherein said rectangular shape andspace have a width and a length greater than said width, and wherein theadequacy of etching or other parameters are determined based on thewidth or length dimensions on said image shape and space.
 7. The processof claim 6 wherein the dimensions of said shape and space are nominallyidentical, and wherein the adequacy of etching or other parameters aredetermined based on the dimensions on said image shape and space.
 8. Theprocess of claim 1 wherein said shape and space have opposed pointsformed by acute angles, and wherein the adequacy of etching or otherparameters are determined as a mathematical function of the distancesbetween the opposed points formed by acute angles on said image shapeand space.
 9. The process of claim 8 wherein said shape and space have awidth and a length greater than said width, and wherein the adequacy offocus or exposure dose parameters are determined based on the width orlength dimensions on said image shape and space.
 10. The process ofclaim 9 wherein the dimensions of said shape and space are nominallyidentical, and wherein the adequacy of etching or other parameters aredetermined based on the dimensions on said image shape and space.